1. Field of the Invention
The present invention relates to a seismic isolation bearing and, more particularly, to a seismic isolation bearing which employs a shock absorbing pad to increase its ability to isolate seismic energy.
2. Description of the Prior Arts
A seismic isolation bearing is a base isolation device provided for protecting various structures from the damaging effects of earthquakes. With reference to FIG. 3, a conventional seismic isolation bearing comprises a lower plate 40 and an upper plate 50 separated by a slider 60. The lower plate 40 has an upward facing concave surface 41. The upper plate 50 has a downward facing concave surface 51. The slider 60 has an upper convex surface 61 that slides along the concave surface 51 of the upper plate 50 and has a lower convex surface 62 that slides along the concave surface 41 of the lower plate 40. When in use, the lower plate 40 rests on the ground base on which the structure to be supported would rest, while that structure rests on the upper plate 50. In the event of an earthquake, the lower plate 40 and the upper plate 50 are intended to move relative to each other via the slider 60 between the lower and upper plates 40, 50. The structure supported is thus isolated from the seismic energy. However, such seismic isolation bearing can only dissipate the horizontal seismic energy. The vertical seismic energy still exists, so that it can still destroy the structure.
With reference to FIG. 4, another conventional seismic isolation bearing comprises a lower plate 70 and an upper plate 80 separated by a slider 90. The lower plate 70 has an upward facing concave surface 71. The upper plate 80 has a downward facing concave surface 81. The slider 90 includes a first member 91 and a second member 92. The first member 91 has an upper convex surface 911, a lower surface and a recess 912. The convex surface 911 slides along the concave surface 81 of the upper plate 80. The recess 912 is formed in the lower surface of the first member 91. The second member 92 has a lower convex surface 921, an upper surface and a projection 922. The convex surface 921 slides along the concave surface 71 of the lower plate 70. The projection 922 extends from the upper surface of the second member 92 and is received in the recess 912 of the first member 91. In the event of an earthquake, the lower plate 70 and the upper plate 80 are intended to move relative to each other via the slider 90 between the lower and upper plates 70, 80 to dissipate the horizontal seismic energy. In addition, the first member 91 and the second member 92 are intended to deflect relative to each other to absorb the vertical seismic energy. However, the first member 91 and the second member 92 are connected only by the recess 912 receiving the projection 922. The connecting area of the first and second members 91, 92 is too small, which causes stress concentration therebetween and thus destroys the first and second members 91, 92.
To overcome the shortcomings, the present invention provides a seismic isolation bearing to mitigate or obviate the aforementioned problems.